The manufacturing process of a laminated plate begins with stacking laminated plate materials to prepare an object that will be compressed. After being delivered between hot platens, the object is applied with heat and pressure by a hot press, or a press, to fluidize and cure thermoplastic resin or thermosetting resin contained in the laminated plate materials to make the materials into one piece.
If the hot platens and the delivered object, which is the object to be compressed, have uneven thickness, thermal strains, temperature nonuniformity and so on in the hot pressing process, uniform temperature and pressure cannot be applied to the object, which will later become a product. As a result, the final product may have defects such as thickness defects, cracks and warpage. In order to resolve the problems including the thickness defects of the products, hot-press cushioning materials (hereinafter, sometimes referred to as simply “cushioning material) are used during press formation.
The cushioning materials are required to have, in addition to the good cushioning properties to resolve the thickness defects and other problems of the products as described above, heat resistance, good releasability from a hot platen in contact therewith, and so on. In terms of releasability improvement, recent cushioning materials sometimes include cushioning-material surface layers (hereinafter, sometimes referred to as simply “surface layer”) over the outer surfaces thereof, in addition to a cushion body with cushioning properties.
Technology related to the hot-press cushioning materials with the surface layers is disclosed in Japanese Unexamined Patent Application Publication Nos. 2004-344962 (Patent Literature 1) and Japanese Patent No. 3221978 (Patent Literature 2).
The hot-press sheet, disclosed in Patent Literature 1, is a cushioning-material surface layer that includes a sheet-shaped base material and a release coating film formed over the base material. The coating film is made of a resin composition in which 5% to 55% by mass of organic powder and 5% to 55% by mass of inorganic powder are mixed in 100% by mass of the resin composition so that the mixture of the organic powder and the inorganic powder becomes 30% to 60% by mass in total. The release coating film formulated as above is intended to prevent formation of sinks and dents in the release coating film on the outer surfaces of the hot-press sheet.
Patent Literature 2 discloses, in terms of heat resistance improvement, a heat-resistant thermo-sensitive adhesive sheet, that corresponds to the cushioning-material surface layer, of a cushioning material used for hot-press formation. The adhesive sheet is made by applying unvulcanized fluororubber over both surfaces of a sheet-shaped base material made of a heat-resistant material and then applying a heat-resistant coating on one of the rubber applied surfaces.
There are also hot-press cushioning materials with aramid cloth for surface layers. The hot-press cushioning materials are configured so that the aramid cloth is disposed on outer surfaces of a sheet-shaped material having cushioning properties.